On Thu, Mar 12, 2009 at 1:15 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >> Timothy Madden wrote: >> > Hello >> > >> > Is -mfpmath=both for i386 and x86-64 still experimental in gcc 4.3, as >> > the in the online manual page ? [...] > > The fundamental problem here is that backend lies to compiler about the > fact that FP operation can not take one operand from SSE and other from > X87. This is something I want to look into once I have more time. With > new RA, perhaps we can drop all these fake constraints.
That would be great ! I am sure having twice the number of registers (sse+387) would make a big difference. Even if SSE and FPU instructions set can not mix operands, using both at the same time (each with its registers) will be an improvement. Until then I would have a question: if I compile with -msse than using -mfpmath=387 would help floating-point operations not steal SSE registers that are already used by CPU operations ? And using -mfpmath=sse would make FPU and CPU share the SSE registers and compete on them ? How would I know if my AMD Sempron 2200+ has separate execution units for SSE and FPU instructions, with independent registers ? Thank you, Timothy Madden
